1. Field of the Invention
The present invention relates to a method for checking the functionability of protective instruction transmission systems in on-line operation in which at least two stations, particularly multi-instruction equipment, are connected by transmission links and communication channels, whereby the stations respectively comprise instruction input and output lines for the transmission of the protective instructions and a first station controlling the checking of the operability transmits a test signal to a second station to be tested, the second station returning the test signal to the first station unaltered.
2. Description of the Prior Art
Protective instruction transmission systems of the type set forth above are most frequently employed in supply concerns, particularly in electrical energy supply networks. Here, it is a matter of recognizing occurring errors within the systems as quickly as possible and limiting the effects of such errors within the network to a minimum. Therefore, for example, given shorts in the high-voltage networks, the affected line sections should be disconnected from the network as quickly as possible (selective protection) in order to avoid greater current outages and, under given conditions, total network interruptions.
Due to the increased pulse-noise insensitivity and the requirement for the greatest possible signal-to-noise ratio, the actual protective instructions are realized, among other things, by way of what is referred to as a multi-frequency keying, i.e., in order to execute a protective instruction keying is undertaken discontinually from the one of the existing frequencies, for example, as a quiescent instruction and is transmitted without interruption and with constant amplitude onto one of the three remaining operating frequencies, whereby the selection of the frequency is dependent on the region to be disconnected or, respectively, on the instruction to be executed.
For further enhancing the reliability of such protective instruction transmission systems, there is the possibility, given selective protection connections, to undertake what are referred to as loop tests in a known manner. A test signal is thereby manually or automatically transmitted from the station to be tested to a cooperating station in the supply network and the latter immediately returns the test signal to the testing station without signal modification. The additionally existing test instructions are subsequently successively transmitted in the same manner and are correspondingly acknowledged. Insofar as there is no inducement for a protective instruction in precisely this time, an undesired triggering and, therefore, the unintentional disconnection of the specific line regions within the network is suppressed.
These and similar switch measures can also be undertaken after telephone consultation between operators at the appertaining stations within the network when it is assured in both stations that no switch instructions can be effectively transmitted during checking of the functionability.
The methods described above, therefore, presume that no protective instruction transmission occurs during the test or, on the other hand, that the enablement of the protective instruction transmission must occur simultaneously in both stations.